Extraction process for recovery of aromatic hydrocarbons utilizing pyridine-bf3 or picoline-bf3 as the solvent



United States EXTRACTION PROCESS FOR RECOVERY OF ARO- MATIC HYDROCARBONSUTILIZING PYRI- DINE-BF OR PICOLINE-BF AS THE SOLVENT Thomas D. Nevitt,Crown Point, ImL, assignor to Standard Oil Company, Chicago, 111., acorporation of Indiana No Drawing. Application March 11, 1955 Serial No.493,815

4 Claims. (Cl. 208-326) tures of aromatic and aliphatic hydrocarbonswhich are commercially produced as processed or unprocessedpetroleumoils or mineral oils, coal tar oils, shale oils and the like.Various aromatic hydrocarbons are valuable as solvents and for thepreparation of resins, plasticizers and various other chemicalderivatives. The removal of aromatic hydrocarbons from varioushydrocarbon stocks may be desired in order to improve their quality forthermal or catalytic cracking,v for hydrogenation operations, for use asheater oils and for other purposes.

With the commercial development of new processes for producing aromatichydrocarbons boiling within the gasoline boiling range bycyclization-dehydrogenation of paraffinic hydrocarbons and by thedehydrogenation of cycloalkanes there has'come an increased demand forprocesses to separate and concentrate the aromatic hydro carbons thusproduced. Thus, with the commercial development of such processes ashydroforming, platinum catalyst reforming of naphthas, and the like, atremendous potential has been createdrfor the production ofnitrationgrade aromatics such as benzene, toluene and xylenes'for use byboth the petroleum and chemical industries. it is an object of myinvention to provide a process for the selective extraction ofhydrocarbon mixtures with specified novel solvents. Another object of myinvention is to provide the art of selective extraction of hydrocarbonmixtures with novel solvents, viz. pyridine-boron trifiuoride orpicoline-boron trifluorides. A further object of my invention is toprovide for the employment of new solvents in a process for theselective extraction of aromatic hydrocarbons from liquid mixturesthereof with aliphatic hydrocarbons, particularly saturatedhydrocarbons. A further object is to provide processes for theconcentration and purification of aromatic hydrocarbons, particularlythose containing not more than about carbon atoms per molecule. Anadditional object is to provide a process for the selective extractionof aromatic hydrocarbons from mixtures thereof with olefinichydrocarbons. Yet another object is to provide a process for theselective extraction of olefinic hydrocarbons from saturatedhydrocarbons. A further object of this invention is to provide a processfor the separation of close-boiling or azeotropic mixtures of aromatichydrocarbons with saturated hydrocarbons by extraction or extractivedistillation with pyridine boron trifluoride or a picoline borontrifluoride. Another object is to provide a process for refininghydrocarbon oils by extractionwith novel solvents. These and otherobjects of my invention will become apparent from the ensuingdescription thereof.

Pyridine-boron trifiuoride is a compound resulting from atenlt gaseousBF for example in a solvent such as dry benzene (Boron Trifiuoride andIts Derivatives, by H. S. Booth and D. R. Martin]ohn Wiley & Sons, Inc.,New York, 1949page 47). The structure of pyridine-boron trifiuoride is:

N F:1'3:;F V 'F in which the substituent methyl is ortho-, metaor paratothe nitrogen atom.

Under otherwise constant operating conditions '(temperature, ratio ofsolvent to feed, extraction temperature, molecular weight of the feedstock, etc.) the solvent power of my novel solvents tends to increasethrough the series: normal parafiins, isoparafiins, cycloparaffins,acyclic olefins, non-conjugated diolefins, cyclic olefins, aromatics andaromatics containing unsaturated substituents. In gen eral, hydrocarbonsof mixed type, for example, alkyl aromatics, have intermediatesolubility to the hydrocarbons of the pure structural components(unsubstituted aromatics and parafiins) In the process of the presentinvention the selective solvent is employed as a liquid, melt orsolution and the feed stock may be charged to the process as a liquid orsolution, or, in some instances, as vapors (extractive distillation).The feed stock is preferably dried by conventional methods such asdistillation or by contact with adsorbents such as alumina or magnesiumsilicates before contacting the selective solvent. 'In extractivedistillation, the temperature should be between the dew point of thehydrocarbon mixture and about 240 C. and contacting of the liquidsolvent and feed vapors is usually in countercurrent. The solventconcentration of the liquid phase in extractive distillation should beabout 5 to about 99 v. percent and the process may be effected atatmospheric or other pressures.

The present extraction process can be applied to numerous hydrocarbonoil fractions derived from petroleum, coal, shale, etc. which are knownto contain aromatic hydrocarbons and relatively polar impurities such asorganic sulfur compounds whose removal is sought in order to producerefined hydrocarbon oils. Such oils may boil within the boiling range of(and the oils may be generally characterized as) gasoline or naphtha,cracked naphthas, coke still naphthas, kerosene, virgin gas oil, crackedgas oil, hydroformer bottoms, heater oil, furnace oil, diesel fuel,transformer oil, crude oil, reduced crude oil, vis-broken crude oil,lubricating oil distillates, etc. The present process may also beapplied to the refining of various coal tar fractions and coal tardistillates, or of the exothermic reaction of one mol each of pyridineand neutralized Fischer-Tropsch process fractions.

Other applications of the extraction process of my invention are in theselective absorption of normally gaseous olefins from their mixture withnormally gaseous paraffinsffor example the selective absorptionof'ethyleue from gaseous hydrocarbon streams containing ethane andmethane, hydrogen, etc., the selective absorption of propylene frompropylene-containing gas streams and the like. My invention is likewiseapplicable to the selective absorption of acetylene from gas mixturescontaining the same and methane, hydrogen, ethane, ethylene, etc. By theemployment of the extraction or absorption process of the presentinvention, it is possible to produce normally gaseous unsaturatedhydrocarbons of high concentration or purity, which is deemed to beextremely desirable in the further treatment or chemical conversion ofsaid hydrocarbons.

In general, liquid-liquid extraction operations can be conducted attemperatures between about C. and about 200 C., more or less, dependingupon the particular charging stock, the particular solvent or solvents,the solventzfeed ratio, the number of extraction stages, the degree ofextraction which is sought, the proportions of auxiliary solvents (ifany), etc., as will be apparent to one skilled in the art. Usuallyliquid-liquid extraction is effected at temperatures between about 30 C.and about 150 C. and in the extraction of naphtha boiling range stocks,I prefer to employ temperatures between about 40 C. and about 80 C.Generally, the selection of a suitable extraction temperature is notcritical.

The ratio of solvent to hydrocarbon feed stock, in liquid-liquidextractions, must be suflicient to exceed its solubility under theextraction conditions in said feed stock in order to form two distinctliquid phases, viz, a raffinate phase containing little or no solventand an immiscible extract phase comprising the solvent and extractedhydrocarbons. Generally, I may employ between about 0.5 and about 50volumes of solvent per volume of hydrocarbon charging stock. Ordinarily,I prefer to employ between about 1 and about 20 volumes of solvent pervolume of feed stock, especially in the treatment of naphtha boilingrange stocks (about 400 F. end-point). Sufficient pressure is maintainedwithin the extraction zone to prevent substantial volatilization of thehydrocarbon charging stock or solvent under the liquid-liquid extractionconditions. It is obvious that pressure and temperature are relatedvariables in the extraction process. Usually pressures within the rangeof about 0 to about 100 psi. are sufficient, it being appreciated thatthe particular pressure which is required in a given case can readily bedetermined by experiment.

Any means of separating extracted materials from the extract phase andof recovering solvent therefrom may be employed. Thus under certainconditions, it may be desirable to distill extracted materials from theextract phase or to wash them out of the extract layer with a paraffinhydrocarbon having a different boiling point. Also, the solvents may insome instances be recovered from the extract layer by crystallization orby Washing with a solvent which is highly selective therefor, such asethers, etc.

The raffinate phase (or in extractive distillation, the distillate) canbe treated by conventional methods to effect further refining thereof.Thus, the raffinate or distillate can be washed with water, aqueousalkalies, etc., treated with adsorbent solids such as activated carbon,activated clays, etc., redistilled, and otherwise prepared for use orsale.

It may be desirable to employ diluents or auxiliary solvents in specificcases in order to modify selectivity of the principal solvent, to lowerthe melting point of the principal solvent to permit its use at lowtemperatures, or for other reasons. The amount of auxiliary solvent canbe selected with reference to specific cases; ordinarily, between about1 and about 20 weight percent or even more, based on the principalsolvent, may be employed. The auxiliary solvent should be miscible tothe desired extent with the principal solvent, and should preferably bea neutral compound. As examples of auxiliary solvents which may beemployed, one may mention the 4 sulfolanes, for example,2,4-dimethylsulfolane, 2,3-dimethylsulfolane and the like; variousnitriles such as acetonitrile, bis-2-cyanoethyl ether and the like;various ethers such as diethyl ether, methyl-tert-butyl ether; glycolsor their ethers having the structure R O(CH CH O),,R and wherein R and Rare alkyl groups and n is an integer having a value between 1 and 3,inclusive, tetrahydrofuran and the like; halogenated hydrocarbonsolvents such as chloroform, carbon tetrachloride, ethylene dichloride,ethylene dibromide, trichloroethane, tetrachloroethane and the like;esters of carbonic acid, monocarboxylic acids, and dicarboxylic acids,for instance, diethyl carbonate, bis-2- hydroxyethyl carbonate,bis-2-chloroethyl carbonate, bis- 2-methoxyethyl carbonate, ethylenecarbonate, n-butyl formate, methyl furoate, dimethyl oxalate, diethylsuccinate, dimethyl phthalate, dimethylisophthalate, and the like;neutral organic nitrogen compounds such as N,N- dialkyl formamides(particularly dimethyl formamide), dimethyl hydantoin and the like,nitro aromatics such as nitrobenzene and the like; ketones, for example,acetone methyl ethyl ketone, methyl isobutyl ketone and the like,aldehydes, for example, furfural, crotonaldehyde and the like;butyrolactone, butyrolactam, etc.

Anti-solvents or diluents may also be employed in the practice of thepresent invention. Thus, diluents such as saturated hydrocarbons,perfluorocarbons, perfiuoroamines, perfiuoroethers, etc. may be added tothe feed stock to be dearomatizedor introduced directly into theextraction zone.

In the extraction, a small proportion of a suitable surface-active agentmay be added to increase the efiiciency of the extraction equipment.Thus long chain esters of perfluoroalkyl alcohols or pertluoroalkylacids, perfiuoroalkyl amides and amines, etc. may be employed, insuitable concentrations between about 0.0001 and about 1 weight percent,based on the weight of the solvent (note G. B. Blake et al.paperpresented before the Division of Petroleum Chemistry of the AmericanChemical Society, September 1954, pp. 313 ff.).

The present invention can be carried out in batch, continuous orsemi-continuous operating cycles, and in one or more actual ortheoretical stages, employing contacting and separation equipment suchas has heretofore been employed in the selective solvent refining ofpetroleum stocks. Various types of liquid-liquid extraction operationsand suitable extraction equipment are described, for example, inChemical Engineers Handbook (McGraw- Hill Publishing Co., Inc., N.Y.,1950), pp. 7'16 if. and 474 ff. It should be understood that thespecific equipment employed forms no part of the present invention andthat any equipment adaptable for the purposes of contacting the solventwith the hydrocarbon charging stock and thereafter separating an extractphase from the refined charging stock can be employed for the purposesof my invention.

The following table shows the results of the extraction of a 50 volumepercent n-heptane-SO volume percent toluene feed with an equal volume ofpyridine-boron trifluoride and 2-picoline-boron trifluoride solvents.Singlestage extractions were effected with solventzhydrocarbon feedratio of one.

The foregoing examples have illustrated specific aspects of myinvention, which is not limited thereto. The extraction process of thepresent invention is readily appliaasenvo cable to the separation ofhydrocarbon mixtures and hydrocarbon types not specifically illustratedin the foregoing examples, e.g., the selective separation of olefinsfrom aromatics, naphthenes from paraflins, naphthenes from aromatics,olefins from saturated hydrocarbons, cycloolefins from acyclic olefins,monoolefins from conjugated diolefins, of conjugated diolefins fromnonconjugated diolefins, of diolefins from aromatics, etc.

Having thus described my invention, what I claim is:

1. A process for the selective extraction of an aromatic hydrocarbonfrom a naphtha fraction containing the same, which process comprisescontacting said naphtha inthe liquid condition with a solvent selectedfrom the group consisting of pyridine-boron trifiuoride and apicolineboron trifluoride, the molar ratio of pyridine and picoline,respectively, to boron trifluoride being one, said solvent being used inan amount sufficient at least to form a distinct liquid phase,separating a raflinate phase from an extract phase comprising saidsolvent and said aromatic hydrocarbon, and distilling said aromatichydrocarbon from said extract phase.

2. The process of claim 1 wherein the extraction is conducted attemperatures between about 40 C. and about 80 C.

3. The process of claim 1 wherein said solvent comprises pyridine-borontrifluoride.

4. The process of claim 1 wherein said solvent comprises apicoline-boron trifluoride.

References Cited in the file of this patent v OTHER REFERENCES BoronTrifluoride and Its Derivatives, Booth and 30 Martin: Published by JohnWiley and Sons, Inc, New

York, 1949, page 47.

1. A PROCESS FOR THE SELECTIVE EXTRACTION OF AN AROMATIC HYDROCARBONFROM A NAPHTHA FRACTION CONTAINING THE SAME, WHICH PROCESS COMPRISESCONTACTING SAID NAPHTHA IN THE LIQUID CONDITION WITH A SOLVENT SELECTEDFROM THE GROUP CONSISTING OF PYRIDINE-BORON TRIFLURORIDE AND APICOLINEBORON TRIFLUORIDE, THE MOLAR RATIO OF PYRIDINE AND PICOLINE,RESPECTIVELY, TO BORON TRIFUORIDE BEING ONE, SAID SOLVENT BEING USED INAN AMOUNT SUFFICIENT AT LEAST TO FORM A DISTINCT LIQUID PHASE,SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE COMPRISING SAIDSOLVENT AND SAID AROMATIC HYDROCARBON, AND DISTILLING SAID AROMATICHYDROCARBON FROM SAID EXTRACT PHASE.